This invention relates to a distance-measuring device installed in a camera, and more particularly to a distance-measuring device for measuring, at high speed, a subject in a to-be-photographed scene.
In general, a camera incorporates a distance-measuring device for measuring a distance to a subject when picking up the subject so as to focus the photography lens of the camera on the subject.
An active-autofocusing system for applying infrared light to a subject to measure a distance thereto from light reflected therefrom (to execute distance measurement), and a passive-autofocusing system for integrating outside light from a subject to measure a distance thereto, are known as distance-measuring devices. These devices generally employ a line sensor or an area sensor as a photoelectric conversion element for receiving image from the outside and converting it into an electric signal.
An artificial retinal LSI device is known as an image processing device using such an area sensor. In this device, an area sensor having two light receiving areas that are positioned to provide a parallax therebetween, and an image processing circuit for executing various types of data processing on an image signal from the area sensor are mounted in a signal IC chip. The image processing circuit executes edge emphasizing (detection), smoothing, one-dimensional projection, etc.
Japanese Patent Application KOKAI Publication No. 8-178637, for example, discloses an image processing device using an artificial retinal LSI, as the artificial retinal LSI device.
This image processing device extracts the outlines of input images, using an artificial retinal element, calculates, at high speed, correlation between outline data on those portions of the outline images, which are located at the same scanning lines, using a correlation computing device incorporating a synapse connection computing circuit, and obtains information such as a distance to an object or movement of the object, on the basis of the computing result.
However, when the image processing device having the artificial retinal LSI disclosed in Japanese Patent Application KOKAI Publication No. 8-178637 is used in a camera, a CPU, which operates at high speed to execute complicated processing, and/or a correlation calculation unit must be mounted in the camera. These units are expensive, and the number of component parts of the distance-measuring device, and hence the size of the distance-measuring device, inevitably increase because of these units.
Moreover, in the above distance-measuring device, two images are input using two cameras having respective artificial retinal LSIs, and the distance to a subject is measured. That is, distance measurement is executed, on the basis of the correlation of the two images using the principle of stereo. Accordingly, the device is large in size and expensive.
This large distance-measuring device can be installed in, for example, a single lens reflex camera, but not in a small and inexpensive machine such as a compact camera.
In different to-be-photographed scenes, if the camera is to photograph different subjects, it should have the ability to focus on different portions of the subjects. For example, if the main subject is a person, the camera should focus on an upper portion, such as the face, of the person. If, on the other hand, the main subject is scenery or a building, the camera should focus on its center.
Usually, however, a distance-measuring point for a shortest distance to an area in which the main subject seems to exist is selected for focusing.
In light of this, there is a technique for detecting a distinctive portion of a main subject in a to-be-photographed scene, and executing appropriate focusing for the main subject.
Japanese Patent Application KOKAI Publication No. 11-25263, for example, discloses a technique for detecting a distinctive point of a subject (area) existing in a to-be-photographed scene, on the basis of the outline of the subject, the distance distribution of the subject, or the actual size of the subject calculated from the distance distribution and the outline of the subject. On the basis of the detection result, exposure time during photography, for example, is controlled.
In the technique for detecting a distinctive point of a subject, disclosed in Japanese Patent Application KOKAI Publication No. 11-25263, determination of a distance-measuring point is especially important.
More specifically, a sensor section for executing distance measurement often has a structure in which pixels consisting of, for example, photoelectric conversion elements are arranged in a matrix or in a plurality of rows. If this so-called sensor array is also used as an image sensor for detecting a distinctive point of a subject, another sensor and its space dedicated to the detection of the distinctive point are not necessary.
Pattern detection for detecting such a distinctive point does not require such accurate detection of a distribution of reflected light as does distance measurement. More easy detection provides a sufficient result. Therefore, if the pattern detection is executed at the same speed as distance measurement, it is a waste of time.